1. Field of the Invention
The present invention pertains to a clamped tool having a cutting insert releasably secured to a tool holder by means of a clamp.
2. Prior Art
FIG. 17 depicts a conventional insert clamped tool which comprises a tool holder 4 having a throwaway cutting insert 1 securely fixed thereto by means of an eccentric pin 2 and a clamp 3. A recess is formed at a forward end of the tool holder 4 to provide an insert-receiving pocket 5 which has a bottom 5a and two angularly-disposed side walls 5b, and an internally threaded bore 6 is formed in the bottom 5a. A seat member 7 is disposed on and fixedly secured to the pocket 5 by means of a screw 2a threadedly engaged with the bore 6, and the cutting insert 1 is placed on the seat member 7. The aforesaid eccentric pin 2 is integrally formed at the top end of the screw 2a, while the clamp 3 is arranged adjacent to the insert-receiving pocket 5. An internally threaded bore 4a is formed in the tool holder 4 so as to be displaced rearwardly of the holder with respect to the seat 5, and the clamp 3 has a hole 3a formed therethrough so as to be internally threaded in a direction opposite to the threads of the bore 4a of the tool holder 4. A double-ended clamp screw 8 having opposite threaded portions is threadedly engaged with these bores 3a and 4a.
For securing the cutting insert 1 to the insert-receiving pocket 5, the eccentric pin 2 is turned in a mounting bore 1a of the insert 1 so that its protrusion 2b is brought into pressing engagement with the inner peripheral surface of the mounting bore 1a. With this operation, the insert 1 is pressed against the side walls 5b of the insert-receiving pocket 5. Then, the clamp screw 8 is screwed into the bores 3a and 4a and tightened to cause the clamp 3 to move downward, so that an abutment face 3a formed at the forward end of the clamp 3 is brought into abutting engagement with the upper face of the insert 1 to press the insert 1 toward the bottom 5a of the pocket 5.
Thus, in the aforesaid conventional tool, the insert 1 is secured by the two-stage operation using the eccentric pin 2 and the clamp 3. Therefore, the clamping operation is not efficient. In addition, inasmuch as the number of the parts required is great, their maintenance is laborious.
In order to overcome the above disadvantages, an insert clamped tool as shown in FIG. 18 has been developed. In this modification, a clamp-securing bore 11, which has an internally threaded portion 11a and a countersunk portion 11b of a greater diameter disposed adjacent thereto, is formed in a tool holder 9 so as to be displaced rearwardly of the holder with respect to an insert-receiving pocket 10. As illustrated, the bore 11 is inclined at a prescribed angle .theta..sub.1 with respect to an axis of an internally threaded bore 12 for securing the seat member to the holder. A clamp 13 is formed so as to have proximal and distal portions 13a and 13b inclined toward each other. The distal portion 13b includes a pressing portion 14 formed at its foremost end so as to have a curved face and an abutting projection 15 formed adjacent to the pressing portion 14, while the proximal portion 13a includes an aperture 16 having internal threads opposite to those of the threaded portion 11a of the inclined bore 11. In this tool, a double-ended clamp screw 17 having opposite threaded portions is screwed into the aperture 16 of the clamp 13 and into the threaded portion 11a of the bore 11, so that the clamp 13 moves along the bore 11. Thus, the insert 18 is pressed toward the bottom 10a of the pocket 10 by the pressing portion 14 and toward the side walls 10d of the pocket 10 by the protrusion 15, whereby the insert 18 can be firmly secured to the pocket 10.
In the above modified clamped tool, the insert 18 can be easily secured to the tool holder 10 simply by turning the clamp 13. However, small areas of the pressing portion 14 and of the protrusion 15 of the clamp 13 contact the insert 18, and besides the insert is usually made of cemented carbide. Accordingly, when the cutting tool is used for a prolonged period of time, the contact portions are susceptible to wearing. Hence, a further tightening of the clamp 13 is required, or the clamp is ultimately damaged.
Furthermore, an optimal clamping force to be exerted from the clamp 13 to the insert 18 is determined by the angle .theta..sub.1 defined between the axis of the inclined bore 11 and that of the threaded bore 12 for securing the seat member. Therefore, the inclined bore 11 must be formed at high precision, resulting in increased manufacturing cost.